Electric translating device



Dec. 27, 1949 R. s. Jol-IN 2,492,429

ELECTRIC TRANSLATING DEVICE Filed Aug. 17, 1945 Patented Dec. 27, 1949ELECTRIC TRANSLATING DEVICE Robert S. John, Waukegan, Ill., assigner toPianstielil Chemical Company, a corporation of Illinois ApplicationAugust 17, 1945, Serial No. 610,975

14 Claims.

This invention relates to a translating device and particularly to a'method of making a translating device for translating mechanicalvariations into electrical variations, and the product prepared thereby.

One object of this invention is to provide an improved translatingdevice made of a flexible material and having a, coating forming anelectrical path with the resistance being varied by strain. Anotherobject is to provide an improved method of making such a translatingdevice so that the resulting product will give uniform results over aWide range of frequencies. Still another object is to provide a simple,efficient, and rapid method of producing such a translating device sothat any desired characteristics may be given thereto. Other objectswill be apparent from the detail description given hereinafter.

The particular translating device described herein is a phonographpick-up of the same general nature as those shown in the Kenneth J.Germeshausen Patents No. 2,329,526, 2,373,676, and 2,380,514, but itwill be understood that the processes here disclosed are applicable totranslating devices in any field where a mechanical movement is to betranslated into an electrical variation.

In practicing this invention I provide a flexible base member having atleast one surface of a flexible insulating material with this basemember being intended to be subjected to mechanical variation. A coatingof finely divided particulate material suspended in a solvent for theflexible insulating surface is applied to this surface. The particulatematerial used is one that is capable of forming a layer whose electricalresistance is varied by strain. This coating is dried, and then a finalcoating of flexible insulating material is applied over thestrain-sensitive coating.

The base member may be made of a flexible insulating materialthroughout, and this is preferably a synthetic elastomer having a lowmodulus of elasticity, such as polystyrene, polymerized methylmethacrylate, or the like. The strainsensitive material is preferablyvery finely divided graphite, such as that made in an electric furnace,and this graphite is applied by suspending it in a solvent for thesynthetic elastomer. Where the elastomer is polystyrene carbontetrachloride is an excellent solvent, as it softens the polystyrene sothat the graphite will be held thereon, but evaporates so rapidly thatthere is no undue penetration and substantially no swelling action onthe polystyrene. Other solvents for polystyrene include toluene, ethylbenzene, ethyl on spring-mounted drying apparatus.

acetate, turpentine, dioxane, gasoline, ethylene chloride, Cellosolveacetate, and paradichlorobenzene. For any given synthetic elastomer asolvent should be chosen that softens the elastomer sufflclently to forman adhesive surface upon which the graphite may be deposited, but shouldalso have a low boiling point so that the solvent will readily evaporatebefore penetrating very deeply into the elastomer.

In making the strain-sensitive coating of graphite on polystyrene, asuspension of graphite in 2 to 3 times its volume of carbontetrachloride is prepared. The polystyrene surface is then dipped inthis suspension and allowed to dry quietly at preferably not more than'70 F. for at least an hour, and preferably for as much as 24 hours, inan atmosphere having low humidity. not over 30% and preferably between10% and 20%. The extra drop that clings to the dipped coating should notbe wiped off, but should be evenly distributed, such as by holding thepolystyrene with the coating in a horizontal position. and slowlyrotating it under conditions where it is substantially entirely freefrom vibration, as

One dipping will produce a very opaque coating of rather highresistance. If the resistance is to be brought down to a lowerpredetermined value successive clippings are made in the same solution,with each coating dried thoroughly before the next is applied. Mypreferred method provides a coating having desired resistancecharacteristics with freedom from noise in operation.

Aifter the strain-sensitive coating has been made, the desired circuitis scribed out and the plastic with the graphite coating is then dippedin a fairly thin lacquer solution and dried. This gives an overallcovering of flexible insulating material. One lacquer that has been usedis made by the Zapon Brevolite Corporation, and is known as XL-44Lacquer. 'I'he active ingredient is elemi, a natural resin. The lacquerto be used should be one that is flexible and that will not causedistortion of the plastic base member. Lacquers other than thatmentioned have these properties and may be used.

When the polystyrene or other synthetic elastomer is successively dippedin the graphite suspension, each dipping should be made as rapidly aspossible, so that some of the graphite put on in previous dippings isnot washed off. The drying which follows each dipping should be done ina dust-free and dry atmosphere, free from drafts, and should be done ata temperature not substantially greater than F. The nal 3 dryin shouldbe continued for at least 24 to 48 hoursas in this time the resistancedrops to a final value and becomes quieter.

The translating device which is the subject of this invention has theflexible portion containing the graphite layer or other strain-sensitivematerial. and usually has another rigid portion that is not flexed. Thisrigid portion ordinarily carries binding posts or the like to whichelectrical leads may be fastened so as to complete the electricalcircuit through the strain-sensitive coating. In the prior patentsmentioned hereinabove this rigid portion was coated with a graphitelayer to complete the circuit. The graphite layer, however, resistedilow of electricity where such resistance was not needed. It has beendiscovered, however, that a superior translating device will be producedif the rigid portion of the device is coated with a layer offreely-conducting material which contacts the layer of strain-sensitivematerial in order to complete the electrical circuit. The conductingmaterial preferably is an oxide-free suspension of metal in a solventfor the synthetic elastomer.

One of the best metals for making conductive coatings is commerciallyprecipitated silver free of silver oxide and having substantially noparticles larger than 200 mesh. This silver may be suspended in 2 or 3times its volume of solvent and applied to the base member with a brushin the desired path. When the elastomer is polystyrene the solvent maybe carbon tetrachloride. The coating of powdered metal should be thickenough to be opaque, usually not less than 0.001 inch.

One embodiment of this invention is shown in the accompanying drawings.Of the drawings Fig. 1 is a side elevation of a translating device madeaccording to the method of this invention; and Fig. 2 is a plan view ofthis translating de- V1(':Ihe translating device I0 shown in theaccompanying drawings comprises a rigid portion li adapted to be mountedon a tone arm o a phonograph or the like, and a beam I2 extendingtherefrom. At the end of the beam there is located a rigidly mountedneedle or stylus I3 adapted to engage the grooves of a record. The beamI2 has a coating of graphite Il arranged in the form of a path extendingfrom near the base II out toward the end of the beam I2 and back to thebase. The beam II has two holes I5 and I6 by which the device may bemounted and which may also be used to provide electrical connections tothe resistance path. From each of these holes there is provided a layerof silver Il with each layer connecting to one end of the graphite path.Thus a complete circuit is formed extending toward the end of the beamI2 that holds the needle I3.

In making the graphite layer I4 the beam I2 is immersed in a graphitesuspension of electrically produced graphite in 2 or 3 times its volumeof carbon tetrachloride. The beam is lmmersed in the suspension aplurality of times, with each immersion followed by complete drying forat least one hour, at a temperature not greater than 70 F. Thesesuccessive immersions are continued until the overall resistance of thegraphite layer is five to eight thousand ohms before scribing and 30,000to 35,000 ohms after the circuit paths have been scribed thereon. Thiscircuit path may be on one or more sides of the beam. The silver layeron the rigid portion II of the translating device is prepared bybrushing 4 on a suspension of finely divided oxide-tree silver in carbontetrachloride. The silver is brushed on in the desired path and asumcient quantity is applied so that the silver layer will be at least0.001 in. thick. The rigid portion is then dried for at least one hourat not more than 70 l".

After the silver and graphite layers have been applied these layers arecovered with a solution of lacquer as described above. 'Ihe lacquerlayer is then dried at a temperature not greater than 70 F. The graphitelayer which prior to the lacquer coating had a resistance oi' 30,000 to35.000 ohms, should now have a resistance o! 60,000 to 80.000 ohms.

The silver coatings may be lightly burnished before the lacquer isapplied. as this improves the conductivity of the silver layers.

The solvent used in making the various suspensions employed inpracticing this invention should be one which dissolves the iiexiblematerial readily but has a rapid rate of evaporation so that thepenetration of the solvent will be very slight. One of the best solventsfor use with polystyrene base members is carbon tetrachloride, whileacetone is an excellent solvent when polymerized methyl methacrylate isused to make the base member. The lacquer used should be one that isfreely exible at all ordinary temperatures, and thatA has no distortingetiect on the base member.

These lacquers, as well as the solvents for the various flexiblematerials that may be used in making the translating devices, and theiruses are well understood by those skilled in the art.

While I have shown and described certain embodiments of my invention, itis to be understood that it is capable of many modifications. Changes,therefore, in the construction and arrangement may be made withoutdeparting from the spirit and scope of the invention as disclosed in theappended claims.

I claim:

1. The method oi making a translating device for translating mechanicalvariations into electrical variations which comprises providing ailexible base member having at least one surface of a flexibleinsulating material, said base member being one that is to be subjectedto mechanical variation, applylng to said surface a coating oi a finelydivided particulate material suspended in a solvent which acts as asolvent for the ilexible insulating surface with said particulatematerial being capable of forming a layer whose electrical resistance isvaried by strain, ydrying the coating at a temperature not substantiallyabove '70 F.. and applying over the coating a layer of flexibleinsulating material.

2. The method of claim 1 wherein the suspension is maintained at atemperature not substantially above 70 F.

3. The method of claim 1 wherein the ilexible insulating surface is asynthetic elastomer and the solvent is one that has a substantiallynonswelling action on the ilexible insulating material and that has arapid rate of evaporation.

4. The method of making a translating device for translating mechanicalvariations into electrical variations which comprises providing ailexible base member having at least one surface of a syntheticelastomer, said base member being one that is to be subjected tomechanical variation, applying to said surface a coating of nely dividedgraphite suspended in a solvent which acts as a solvent for theelastomer while maintaining the suspension at a temperature notsubstantially above 70 F., said solvent being one that has asubstantially non-swelling action on the elastomer and that has a rapidrate of evaporation, drying the coating at a temperature notsubstantially above 70 F. and at low humidity, ap-

plying over the coating a solution of a exible insulating material, anddrying..

` 5. The method of claim 4 wherein the synthetic elastomer ispolystyrene and the solvent is carbon tetrachloride.

6. The method of claim 4 wherein the solution of flexible insulatingmaterial is a lacquer that has substantially no effect on the dimensionsof the synthetic elastomer. 7.. The method of making a translatingdevice for translating mechanical variations into electrical variationswhich comprises providing a base member of polystyrene that is to besubjected to mechanical variation, applying to at least one surface ofsaid base member a coating of finely divided graphite suspended -incarbon tetrachloride that is maintained at a temperature notsubstantially above 70 F., drying at a temperature not substantiallyabove 70 F. and at low huI midity, applying over the coating a lacquerthat has substantially no effect on the dimensions oi' the polystyrene,and drying.

-8. The method of claim 7 wherein the graphite is applied to the basemember by a plurality of dipping operations with substantially completedrying of each coating before applying the next one, with the dippingoperations being continued until there is a iinal resistance of 30,000to 35,000 ohms, after scraping and scribing.

9. The method of making a translating device for translating mechanicalvariations into electrical variations which comprises providing aflexible base vmember having at least one surface of a ilexibleinsulating material, said base member v being one that isto be subjectedto mechanical variation, applying to said surface a coating of a finelydivided vparticulate, material suspended in a solvent which is a solventfor the ilexible insulating surface by successive applications of saidsuspension with each application followed by drying, said particulatematerial being capable of forming a layer whose electrical resistance isvaried by strain, and applying over the final coating a layer ofilexibleinsulating material.

10. The method of claim 9 wherein each application is 'an immersion andis dried at a temperature not substantially above '10 F. forapproximately 24 hours.

11. The method of claim 9 wherein the suspension is maintained at atemperature not substantially above 70 F., and each immersion is driedat a temperature not substantially above 70 F. for approximately 24hours.

12. The method of making a translating device for translating mechanicalvariations into electrical variations which comprises providing a basemember of polystyrene having one portion to be subjected to flexing andanother portion to be held substantially rigid, coating the flexibleportion with graphite suspended in carbon tetraoh1oride, drying, coatingthe rigid portion with a suspension of nely divided oxide-free silver incarbon tetrachloride with no particles of the silver being larger than200 mesh,5 drying, said coatings overlapping at their adjacent edges toform a continuous electrical path, covering said coatings with alacquer, and drying.

13. The method of claim 12 wherein the suspensions are maintained at atemperature not substantially above 70 F., and the coatings are dried ata temperature not substantially above 70 F.

14. The method of claim 4 wherein the solution of Vflexible insulatingmaterial causes the resistance of the coating of graphite to be substanetially doubled.

ROBERT s. JOHN.

REFERENCES curan The following references are of record in the file ofthis'patent:

UNITED STATES PATENTS 211,324 Great Britain Rb. 21,1924

